Electric brakes include one or more electromagnetic actuators (EMA's) for producing a braking force. EMA's may include a motor that turns a ballnut/ballscrew assembly to change the position of a piston and develop an output force at the outward end of the piston that presses against a brake. Such electric brakes may be used, for example, on aircraft wheels, and will be described herein in terms of use on an aircraft. The invention discussed herein, is not, however, limited to use on aircraft and may be used in connection with other electric braking systems as well.
Internal friction in an electric brake, in the ballnut/ballscrew assembly, for example, must be overcome to move the EMA piston. Therefore the output force exerted by a piston against a brake is generally less than the force developed by the motor. Up to 30% of the motor force output may be required to overcome internal friction. Even when applying a static force, the internal friction in the EMA resists the EMA in maintaining the desired force against the brake. Therefore, the level of power delivered to the EMA must be adequate to overcome the internal friction of the EMA and produce the desired output force at the piston.
Aircraft brakes are often required to apply and hold a large static force, for example, when testing the engines prior to takeoff. Electromechanically actuated brakes require power to hold a static force. The power required increases (or decreases) as the square of the desired force. Moreover, the higher the power level applied, the more heating will be experienced by the EMA. It would therefore be desirable to reduce EMA power requirements when maintaining a desired force output.